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Etching brass with ferric chloride, What to use as a resist?

Im etching some brass shells with ferric chloride, but i'm torn on what to use as a resist. I'[m leaning towards krylon paint, but im thinking that would take forever to take off once the process is over. any suggestions as to what will hold up but not eat up all my labor time in removal?

Dan, that is the Holy Grail of etching. Rodne has probably done more etching than most of us and I know he is still searching for something better for a resist. I've done lots of R&D (mostly R) on the topic but there does not seem to be anything that is optimum for laser engraving. Quite honestly, I don't think removal of the "paint" after the etching is the biggest problem. The problems are: 1) getting the resist to adhere well in the first place - not so easy with brass and copper 2) finding a material that will laser off CLEANLY i.e. not leave a residue. 3) finding a material that will laser at high resolution and not chip off leaving rough edges.

Most paints, lacquers, etc will leave a residue of some sort after lasering. You can mechanically abrade after lasering, or use a chemical to remove the residue. Both options run the risk of also removing or compromising the resist. But if you don't remove the residue you will get poor and inconsistent etching.

There are various paint removers and solvents that will remove the paint after etching. I think 3M makes a stripper that isn't too nasty. Brake fluid may work for some products. Of course you have to deal with disposal issues with any chemicals you use.

I have about 15 cans of different paints here which I know won't work - at least, not they way I want. But I don't have the time and resources of Edison . . .

In a previous life, I was a printmaking major in Art school. We used asphaltum as a resist on metal plates of all kinds and could get very fine detail with acid and a feather (for agitation, silly). Of course, we made our intaglio images by mechanically removing the ground, drawing with a needle. I don't know how it would react to a laser, just thought I'd throw this out there.

BUT, the other thing we used was hairspray (lacquer) for making aquatints... might be something to try? It's clear and easy to remove with no residue.

Greg Bednar started a thread recently related to selective plating which used some kind of asphaltum as the resist. I watched the video and it looked like they lasered it successfully, then plated it. So it was used as a plating mask, not an etch mask. It may work as an etch mask as well. But I never figured out exactly from the video and the responses to the thread what was actually used . . .

Applying asphaltum

If anyone wants to try it:
Materials:

Asphaltum ground

An inexpensive 1" brush

Whiting or a substitute cleanser.

Procedure:
The plate must be cleaned of oil, grease and fingerprints that may keep the ground from adhering to the metal. Whiting or a cleanser is used for this purpose. When the plate will accept a smooth film of water we can assume that all contaminates have been removed.
After the plate has been dried with paper towels, brush a thin even coat of asphaltum on the plate. You can either allow the plate to dry on its own or you can place it on the hot plate at a low heat (150 - 200) to speed up the drying.

Asphaltum ground (also known as "hard ground") can be bought at art supply places like Dick Blick... and it IS an etching mask.

You can laser asphaltum but it won't come off cleanly in one pass, it will likely take multiple passes. You can increase power and try for faster removal but you will lose detail that way. I found black krylon to work much better and lasered off much cleaner. My customer was etching copper plates with some pretty fine detail and the krylon/laser option worked really well for him. After etching he used mineral spirits or paint remover, not sure which, to remove the krylon.

Gary

I have done so much with so little for so long, that I can do almost anything with practically nothing...

ASPHALTUM! Thanks Dee! I've been racking my brain to figure out what it was i used when i was in printmaking at school. Thats how i came up with the acid etching idea. Actually using my degree, who knew? I ran some tests and krylon comes off pretty easily with DNA. the only problem is getting it to stick, but i think a few coats will do. Plus, i need to have them done by mid next week, si i guess im running out of time lol. thanks guys for the info!!

We use polyester based laser friendly vinyl but your major problem is gonna be residues lasers leave behind. You can even use a permanent marker pen as a resist - same problem , laser wont leave totally bare etchable surfaces. I sandblast after lasering to remove residues , hence the resist ALSO has to withstand blasting. I have written a lot about etching on this forum , search for etching or ferric or resist

Paints worked for me too - sort of.
The issue vs PCB's (which have a very thin metal layer) is that we do deep etching of brass and stainless and even using the edinburgh etch formula (using citric acid in the FeCl) the etch needs to be heated and sprayed to get any depth capable of being paint filled etc. The hot etchant soon removed the insides of small letters (even after using an etch primer and an overspray of car enamel)
Trying the etchant cold meant many hours of etch time and the paints lifted badly , undercutting is a problem in that scenario.
The laser still left a teeny residue when ablating paint , but I just used to wash the unetched plate with diluted " Handy Andy " (household abraisive cream) prior to etching and gently rub it with my fingers - worked well to clear the etched sections to bare metal.
I used to use chromic acid as a mordant (etchant) on brass , it leaves a wonderful frosted crushed finish - used a "sharpie" as a resist (permanent marker) as well as those rub on letraset letters , however the finish was purely decorative and had no depth to speak of.

If you have a PCB shop nearby you can ask to talk to one of their engineers and see if they have any ideas although their masks are meant to stay on and are typically a photoimageable liquid. Occasionally we used to get peelable mask applied to circuit boards, but this was to mask holes in the wave solder process. I'm not sure if it would work in the etching process.

Dan, you will need to have a comprehensive cleaning procedure to prepare the brass before painting. As Rodne noted, if you get any small parts of the resist falling off, you will have a reject. I would include an abrasion step at the beginning using 600 grit (minimum) wet/dry - but use water. Perhaps even higher grit such as 1000 or 1200, or else work up to that grit. Follow that by washing in hot soapy water. The surface must be completely wetted with no beading.

If you use solvents you should not use paint thinners or kerosene etc as they leave oily residue. Also avoid the "Brasso" type cleaners as you will get residual deposits. There are some chemical pretreatments that might be suitable to get the paint to adhere better. Test before use as some may cause discoloration of the brass e.g turn it pink (which is normal for clean copper.) If you can polish it back to shiny brass after etching that might not be a problem, but you may need a coat of clear lacquer to prevent tarnishing.

For very light etching you may be able to get away with a less stringent cleaning procedure, as you will not be immersed in the ferric for very long. But if you can't afford rejects the cleaning may be warranted.

I know you wanted to minimize labor but with etching there are a lot of steps involved to do it well.